1. Field of the Invention
This invention relates to an improved process and a device for the recovery of certain elements from used nuclear reactor fuels, and, more specifically, this invention relates to an improved process and a device to recover minor actinides and transuranic elements from spent nuclear fuel in an electrolytic salt bath.
2. Background of the Invention
Typical electrochemical processes to recover uranium from spent nuclear fuel result in the accumulation of minor actinides (americium (Am) and curium (Cu)) and transuranic elements (plutonium (Pu) and neptunium (Np)). These accumulated elements usually occur as metal chlorides in the molten electrolytic salt. They must periodically be removed from the electrolyte for the fuel reprocessing to continue.
The simplest method to recover the target elements is via chemical or electrochemical reduction. Electrochemical reduction has two advantages over chemical reduction. The first advantage is that the site of reduction is localized to the cathode surface forming a cathode deposit affording easy removal from the process equipment. The second advantage is that the use of electrons as the reducing agent does not add to the waste volume. Deposition of the transuranic elements and minor actinides on a solid cathode is well-known. Accompanying anode reactions include the oxidation of chloride ions to chlorine gas, oxidation of a sacrificial alloy, and oxidation of metallic uranium or reduced light water reactor (LWR) feed material.
Some electrorefiner pyroprocessing methods for MA's and, in particular, TRU's include the use of liquid cadmium (Cd) electrodes to reduce TRU's along with some uranium (U). FIG. 1 is a schematic diagram of the basic concepts of a cadmium electrode electrorefining system depicted as numeral 10. Chopped spent fuel 12 is placed in a ferric metal anode basket 14 which rests in an eutectic salt bath mixture of LiCl—KCl 16. Uranium and TRU's are anodically dissolved via oxidation with some uranium being reduced to metal 18 at a solid cathode 20. The remaining uranium and the TRU's are reduced and collected in/at a liquid cadmium cathode 22. The TRU's are stabilized in the liquid cadmium cathode 22 due to their low activity coefficients. Fission products such as alkali, alkaline earth and rare earth metals are dispersed within the salt bath 16. Noble metal fission products typically remain in the anode basket 14. Other electrorefining pyroprocessing methods for MAs and TRUs use ferric metals such as carbon steel as cathodes. Preferential deposition of MAs and TRUs over uranium at the cathode would eliminate many processing steps to separate the uranium from the MAs and TRUs.
U.S. Pat. No. 4,824,743 awarded to Fuji, et al. on Apr. 25, 1989 discloses an ion-exchange porous, secondary battery separation membrane.
U.S. Pat. No. 4,397,908 awarded to Philips on Aug. 9, 1983 discloses an electrically neutral non-permselective porous membrane which can transmit negatively and positively charged ions between electrodes.
None of the aforementioned patents disclose a method for the electrorefining of minor actinides and transuranics which uses only solid electrodes and has nonvolatile, noncorrosive products.
A need exists in the art for a method and device for more efficient, safer, and more facile electrorefining of minor actinides and transuranic elements. In addition, a need exists for a method and device which uses only solid electrodes and gives only nonvolatile, noncorrosive products.